The studies outlined in this proposal are designed to provide information which will contribute to our understanding as to whether specific fatty acids play different roles in the maintenance of proper membrane function. The objectives of this research are to: 1) measure the turnover rates of the various fatty acids as well as of glycerol as found in the various molecular species of choline and ethanolamine phosphoglycerides as isolated from rat liver. The acids to be used in this study are palmitic, stearic, oleic, linoleic, eicosa-8,11,14-trienoic, eicosa-5,8,11 trienoic and arachidonic acids: 2) to measure what influence dietary modification has on altering the turnover rates of the above fatty acids and glycerol; 3) to determine whether phospholipase A or phospholipase C treatment of microsomes and mitochondria isolated from rats raised on both balanced and fat free diets are selective for specific fatty acids or given molecular species; 4) to determine whether there is a positive correlation between in vivo turnover rates of fatty acids and molecular species and susceptibility to attack by phospholipase A and phospholipase C. Turnover rates will be measureed according to the following general procedures. Radioactive glycerol or a radioactive acid will be injected into rats and the rats will then be sacrificed after various time periods. Liver choline and ethanolamine phosphoglycerides will be isolated, converted to diglycerides and then to diacylacetylglycerols and fractionated into molecular species by argentation thin layer chromatography (TLC) and reversed phase TLC. Molar amounts of each molecular species will be determined and after suitable corrections for radioactivity not due to the injected isotope, the log of the specific activity will be plotted versus time to compute the turnover rate of the injected isotope in the various molecular species.